1. Field of the Invention
The present invention relates to mold cavities and mold cavity inserts made of polymers, metals, and combinations thereof, that can be used in a variety of molding applications, while being particularly suited for applications demanding fine mold reproduction, as well as expedient and cost-effective mold cavity interchangeability. More specifically, the present invention relates to mold cavities and mold cavity inserts for golf ball manufacturing.
2. Description of the Related Art
Mold cavities are used to manufacture the dimpled cover portions of golf balls. Until the present invention, mold cavities used for making the dimpled cover portions of golf balls have been made of metal. The shapes, dimensions, and pattern of the dimples on a golf ball significantly contribute to the aerodynamic performance of the ball as shown by windtunnel testing and performance testing using robots and golfers. For this reason, golf ball manufacturers routinely experiment with varieties of new and different dimple patterns, shapes, and sizes, in order to arrive at designs that enhance golf ball performance. Achieving the desired aerodynamic performance properties requires the ability to produce such dimensions, shapes, and patterns consistently with careful attention to producing uniform geometry and dimensions across the dimples for a given ball design. As a result, there is a demand in the golf ball industry for producing intricate and novel dimple shapes and patterns with the ability to consistently, accurately, and reliably reproduce such designs. Because a golf ball receives its dimples from a mold cavity, the integrity and characteristics of the dimples formed on the golf ball are dependent upon the accuracy of the mold cavity from which the dimples are formed.
While it is important that precise and well-formed golf ball mold cavities be available for manufacturing golf balls, it is also desirable that golf ball manufacturers have the ability to quickly test and evaluate golf balls exhibiting new and different dimple patterns and features which, necessarily, requires the ability to quickly form the mold cavities used in their creation.
In addition to producing golf balls with different dimple patterns quickly, a golf ball manufacturer may also want to evaluate numerous dimple patterns at the same time. This requires not only that the mold cavities used in their creation be formed quickly, but also that the mold cavities be formed in a cost-effective manner. Further, mold cavities that are less expensive to produce and that are conveniently replaceable or interchangeable, allow greater flexibility and improved cost control in producing prototype golf balls for testing as well as in larger scale golf ball production for sale.
Typically, the dimpled cover portion of a golf ball is made using a molding process such as injection molding, compression molding or casting. Commonly, two oppositely facing mold halves are used, an upper mold half and a lower mold half, with each mold half having a hemispherical, inversely dimpled mold cavity formed out of metal. Each mold half is approximately one half of the size of a finished ball. It is an industry standard to make inversely dimpled mold cavities used for making golf balls out of metal, typically stainless steel. Harder metals, like stainless steel, are chosen primarily because of their durability, mechanical strength, and ability to withstand higher pressures and temperatures without deforming. When the two mold halves are put together they form an internal cavity that is generally spherical with an inversely dimpled pattern representing the negative image of the dimple pattern that will be produced on the golf ball formed therein. U.S. Pat. No. 4,552,004 describes this process and also describes typical methods used for forming golf ball mold cavities, namely hobbing, die-forming, and a high-pressure hydraulic press method. Notably, though, there are significant drawbacks and limitations associated with each of these methods and the mold cavities they produce.
As described in U.S. Pat. No. 4,552,004, the disadvantage of hobbing is that the metal used to make the mold must be very soft in order to flow well enough to adequately conform to the hob. Further a mold made by hobbing has a short useful life because it is soft and susceptible to deformation and damage when manufacturing loads are applied. Also as described in U.S. Pat. No. 4,552,004, while the die-forming process for making golf ball molds has the advantage of being able to utilize harder metals like stainless steel, and thereby providing greater durability, the dimples formed are generally less accurate than those made by hobbing. Less accuracy in dimple formation is disadvantageous because it causes greater variation in the dimples produced from mold to mold which effects the aerodynamics of a golf ball.
The high-pressure hydraulic press method disclosed in U.S. Pat. No. 4,552,004 is designed for making mold cavities out of hard metals (due to the extreme pressures involved) with the aim of providing durability advantages similar to those found in die-forming. However, a disadvantage in using the high-pressure hydraulic press method is that the dimpled master model (resembling the dimple pattern of the golf ball to be formed) upon which the inversely dimpled mold cavity shell is formed, must be of an extremely hard metal (for example, pre-hardened steel) in order to resist deformation under the extreme pressure applied. U.S. Pat. No. 4,552,004 indicates that generally the required pressure will be in excess of 100,000 p.s.i. A significant disadvantage in using a dimpled master model made of a very hard metal is that it takes much longer to machine a very hard metal compared to softer materials. It can take sixteen hours or more to machine a dimpled master model made of HD-13 pre-hardened steel. In addition, the tool bits used to machine such a hard metal must be of very high quality and durability, making them expensive. It is typical to consume several tool bits for each dimpled master model made, as they wear out during the machining process.
Once an inversely dimpled mold cavity shell is formed, it is typical in the industry to then braze the mold cavity shell into a metal retaining cup which provides support and acts to hold the mold cavity shell in place during golf ball molding. The inversely dimpled mold cavity shell then undergoes a machining finish and polishing process. The brazing, finishing, and polishing process typically takes about three hours to complete. Two of these inversely dimpled mold cavity shell and retaining cup assemblies are then aligned opposite one another in a mold base and when the two are closed, they form a substantially spherical cavity used to mold a golf ball.
It is common in the golf ball industry for golf ball manufacturers to order inversely dimpled mold cavity shell and retainer cup assemblies made of steel (or other metals) from machine shops that support the industry. Typically a computer-aided-design (CAD) dimple pattern model is provided to a machine shop and a lead-time of ten weeks or more is typical before the mold cavity shell and retainer cup assemblies are received.
The extended amount of time required by using presently known techniques for obtaining golf ball mold cavities (especially for testing and prototyping when many designs are being considered and when designs are changing rapidly) is a bottleneck for manufacturers interested in bringing new designs to market rapidly. Further, production molding is more expensive and flexibility is limited by the presently known techniques utilizing metal mold cavity inserts that are brazed into metal retaining cup housings. The presently known methods prevent mold cavity inserts from being removed from a production line without removing the retaining cup housings as well, and metal components are generally more expensive to make than plastic components.
Therefore, a need exists for replaceable mold cavities and mold cavity inserts that can be produced less expensively and more rapidly than the presently known techniques for making golf ball mold cavities. The replaceable mold cavities and mold cavity inserts must also provide the requisite exactness and uniformity in dimple size, shape, and pattern and provide the strength and durability characteristics required during the elevated temperatures and pressures commonly used during golf ball molding.